Expandable polymer mixtures composed of styrene polymers, polyolefins, and optionally solubilizers, such as hydrogenated styrene-butadiene block copolymers, are known by way of example from DE 24 13 375, DE 24 13 408, or DE 38 14 783. The foams obtainable therefrom are intended to have better mechanical properties when compared with foams composed of styrene polymers, in particular better elasticity and less brittleness at low temperatures, and also resistance to solvents, such as ethyl acetate and toluene. However, the ability to retain blowing agent and the foamability of the expandable polymer mixtures to give low densities are inadequate to meet the requirements of processing.
WO 2005/056652 describes molded foams with density in the range from 10 to 100 g/l which are obtainable via fusion of prefoamed foam beads derived from expandable, thermoplastic polymer pellets. The polymer pellets comprise mixtures composed of styrene polymers and of other thermoplastic polymers, and can be obtained via melt impregnation and subsequent pressurized underwater pelletization.
Elastic moldable foams composed of expandable interpolymer beads are also known (e.g. US 2004/0152795 A1). The interpolymers are obtainable via polymerization of styrene in the presence of polyolefins in aqueous suspension, and form an interpenetrating network composed of styrene polymers and of olefin polymers. However, the blowing agent diffuses rapidly out of the expandable polymer beads, and they therefore have to be stored at low temperatures, and have only a short period of adequate foamability.
WO 2005/092959 describes nanoporous polymer foams which are obtainable from multiphase polymer mixtures which comprise blowing agent and which have domains in the range from 5 to 200 nm. The domains are preferably composed of a core-shell particle obtainable via emulsion polymerization, and the solubility of the blowing agent in these is at least twice as high as in the adjacent phases.